Electrically-conductive ceramic-metallic protective coating

ABSTRACT

Compositions having essentially only ceramic and metallic constituents are provided for application to metal parts by conventional oxyacetylene flame spraying equipment or plasma arc spraying equipment to develop an adhering electrically-conductive protective coating to thereby provide improved metal part resistance to surface corrosion attack.

United States Patent [191 Michael [111] 3,821,019 June 28, 1974 1 ELECTRICALLY-CONDUCTIVE CERAMIC-METALLIC PROTECTIVE COATING [75] Inventor: Harold J. Michael, Columbus, Ohio [73] Assignee: Rockwell International Corporation,

7 Pittsburgh, Pa.

[22] Filed: Mar. 6, 1972 [21] Appl. No: 232,302

Related US. Application Data [62] Division of Ser. No. 93,493, Nov. 27, 1970, Pat. No.

29/195; 75/94; 148/26; 219/146; 1l7/l05.2, 46 PS, 22, 129, 93.1 PF

[56] References Cited UNITED STATES PATENTS 2,697,159 12/1954 Donahey 106/313 2,745,769 5/1956 Linnert et a]. 117/129 2,775,531 12/1956 Montgomery et a1. 117/22 2,848,349 8/1958 Rechter et a1. 1 17/1052 2,904,449 9/1959 Bradstreet ll7/l05.2 3,322,515 5/1967 Ditt rica et 111 29/1912 3,388,001 6/1968 Blum et a1. l 17/105,?- 3,397,080 8/1968 Girard et al. 117/1052 3,607,343 9/1971 Longo et a1 l17/l05.2 3,702,770 11/1972 Michael l17/l05.2 3,706,579 12/1972 Michael 106/1 FOREIGN PATENTS OR APPLICATIONS 1,080,383 4/1960 Germany 219/146 OTHER PUBLICATIONS E. Levin et al., Phase Diagrams for Ceramists, Co1umbus, 1964, p. 172 (LiAO-SiO2-Ti02).

Primary Examiner-Michael Sofocleous [57] ABSTRACT Compositions having essentially only ceramic and me tallic constituents are provided for application to metal parts by conventional oxyacetylene flame spraying equipment or plasma arc spraying equipment to develop an adhering electrically-conductive protective coating to thereby provide improved metal part resistance to surface corrosion attack.

6 Claims, No Drawings ELECTRlCALLY-CONDUCTIVE CERAMIC-METALLIC PROTECTIVE COATING CROSS-REFERENCE This is a division, of application Ser. No. 93,493, filed Nov. 27, 1970, now US Pat. No. 3,702,770.

SUMMARY OF THE INVENTION Aluminum metal powder is mixed in prescribed proportions with a finely divided alkali titanate compound,

such as lithium-silico-titanate (lithium titanium sili- DETAILED DESCRIPTION The following general formulation identifies the principal constituents, by range and on a 100 parts by weight basis, of the ceramic-metallic protective coating compositions of this invention:

COATING COM POSITIONS Constituent Range Aluminum metal powder. "120 +325 mesh. spherical particles, ill) Alkali titanate compound, 20 80 l 20+325 mesh frit,

'I'Al.

Details regarding each of the principal constituents, and particularly methods for formulating and preparing certain of such principal constituents, are provided in those portions of the detailed description which follow.

Adjustments may be made to the composition formulation within the ranges indicated to vary the degree of resistance to weathering and corrosion attach obtained for particular metal parts coated with the instant composition and also to vary the ease of application obtained with conventional spraying equipment of the oxyacetylene type or plasma arc type as a function of the composition wetting property.

ALUMINUM POWDER CONSTITUENT The ceramic-metallic composition of this invention utilizes -l 20 mesh +325 mesh aluminum powder such as is commonly purchased commercially in a spray grade form, such metal powder having particles which are substantially spherical in configuration.

ALKALI Tl'lANATE COMPOUND CONSTITUENT One preferred alkali titanate compound constituent is lithium-silico-titanate, sometimes referred to herein as lithium titanium silicate, an essentially nonhomogeneous opalescent glass having two distinct compositional phases in both the liquid conditionand the solid condition. Such constituent is preferably compounded to have a 1:111 molecular ratio of Li O to SiO to TiO and may be made in the, following manner.

The Example I ingredients given below, stated on a 100 parts total weight basis, are combined by thorough dry blending, smelted at 2,000 F. 2,300 F and fritted to form the preferred lithium-silico-titanate compound constituent:

EXAMPLE I CONSTITUENT COMPOSITION Preferred Component Range Amount Silica (SiO 20.0 80.0 28.2 Titania (TiO,) 20.0 80,0 37.3 Lithium Carbonate(Li CO.-i) 114-740 in TOTAL 100.0 100.0

Preferred Oxide Range Amount Li .0 l7.6 TiO 20- 470 so a- 2 TOTAL I000 100.0

Another alkali titanate compound constituent satisfactory for practice of this invention is lithium titanate. Such may be included in the compositions ofthis invention optionally or additionally with respect to lithiumsilico-titanate, for example. If provided by way of addition, the compound functions to furhter decrease the electrical surface resistivity property of the final coating to thereby develop improved anodic protection for the resulting coated metal part. The below detailed lithium titanate constituent, however, does not in most cases alone provide optimum surface wetting during application of the composition to metal parts by flame spraying. Such lithium titanate constituent is compounded to have a preferred l:l molecular ratio of TiO to U0 and may be made from the following Example II ingredients, detailed on a parts total weight basis:

EXAMPLE [I CONSTITUENT COMPOSITION Preferred Component Amount Lithium (arhonatc [I.i-,(():,) 48.1 Titania (TIOU 5 .9 I'O'IAl. 100.0

alternatively be melted at a temperature of approximately 2,300 F. :t 50 F. and fritted in lieu of being fused into clinker form for the subsequent processing.

The resulting ground clinker or frit is graded to pass a No. 120 U.S. standard sieve and remain on a No. 325 U.S. standard sieve for use. As in the case of the lithium titanium silicate constituent, particles larger than 120 mesh may be further ground for use; particles of a 325 mesh size may be re-charged into subsequent lithium titanate constituent batches as cullet for retiring.

It should be noted that other alkali titanates may be used in the coating composition formulations although lithium titanate compounds are preferred inasmuch as lithium is more electro-positive and provides superior anodic protection in comparison to other alkali metal titanates such as sodium titanate or potassium titanate or in comparison to alkali earth metal titanates such as the titanates of magnesium, calcium, strontium, or barium. Stated in another manner, lithium titanate compounds appear to particularly enhance or improve the electrical surface conductivity of the applied coating.

The following Example III, Example IV, and Example V coating composition formulations, given on a 100 parts by total weight basis, are examples of embodiments of this invention that have been utilized for satisfactorily developing improved resistance to corrosion attack for metal parts to which the composition has been applied.

EXAMPLE III COATING COMPOSITION Preferred Constituent Amount Aluminum metal powder, -l20 +325 mesh spherical particles. 40 Lithium-silico-titanate, l 20 +325 mesh frit, 40 Lithium titanate (Li TiO;,), 120+325 mesh rm. 20 TOTAL I EXAMPLE IV COATING COMPOSITION Preferred Constituent Amount Aluminum metal powder, -l20 +325 mesh spherical particles, 50 Lithium-silieotitanate, 20 +325 mesh lrit, 50 TOTAL I00 EXAMPLE V COATING COMPOSITION Preferred Constituent Amount Aluminum metal powder. I2() +325 mesh spherical particles, 50 Lithium titanate (Li TiO |20 +325 mesh rm, TOTAL I00 In either case, however, it is necessary that the metal part, which may be a large mild steel structural part by way of example, should be cleaned by mechanical means in those areas which are to be coated. Cleaning may be accomplished either by abrasive blasting using a 40 mesh clean sand or alundum grit, by disc sanding, or by stiff wire brushing. The areas to be coated basically must be free of oxide, scale, welding flux, and other foreign material prior to application of the coating composition. Since roughened, clean metal surface is essential to good adherence, any loose particles should therefore be removed from the metal part surface as by blowing using clean, dry, compressed air.

Using conventional oxyacetylene flame spray equipment, by way of example a Metco powder spray gun with a ceramic material feed nozzle having a No. 2 feed orifice, the compositions are applied by box or cross coating the metal part practicing the following steps. First, and prior to starting the flow of composition through the gun, preheat the surface to be initially sprayed by passing the gun flame over the surface at a distance of from 6 inches to 8 inches thereby accomplishing a degree of pre-heating. Next, composition flow is started, adopting the equipment manufacturers control setting recommendations as to feed setting, oxygen flow, and acetylene flow, and application is accomplished by spraying the metal part surface using horizontal straight-line rather than arc-type motion with the composition material impinging upon the metal part surface at as near a angle as possible. After the pre-heating has been accomplished with respect to the area to be initially coated, the remainder of the metal part is normally automatically pre-heated as the spraying work progresses. Adequate coverage of the metal part is usually obtained using one cross or box coat with a composition deposit density of from 20 to 23 grams of composition per square foot of metal part surface. Care must be taken that the speed of application is not so fast as to produce a loose, powderytype coating. Normally non-porous coating is obtained with gun travel over the work at a velocity of not more than four feet per minute.

The non-porous composition coating as sprayed has excellent bond in adhesion as well as cohesion. The coating composition as sprayed provides excellent long time anodic protection for numerous different ferrous metals, stainless steels, and nickle-base alloys exposed to salt corrosion environments. In some cases (Example I, Example III formulations) the applied intermetallic compound coating has essentially a zero resistance to electrical current flow with as little as 40 percent to 50 percent by weight aluminum metal content. In addition, the coating has outstanding resistance to impact, bending, or deformation failure by virtue of a high degree of inherent ductility. The coating is compatible with fused-on type of cermet protective coatings, such as the coatings detailed in my co-pending Application for U.S. Letters Patent Ser. No. 69,914 filed Sept. 4, 1970 (a continuation-in-part of Application for United States Letters Patent Ser. No. 833,698, filed June 16, 1969 and assigned to the assignee of this application), now U.S. Letters Pat. No. 3,706,579 granted Dec. 19, 1972, and has also been successfully applied over conventional welds that serve to join two metal parts previously coated with such fused-on type of cermet protective coatings.

I claim:

1. The method of providing a metal surface with an adhered, highly-conductive protective coating comprising the steps of:

a. Combining, on a 100 parts total weight basis, from to 80 parts aluminum metal in finely divided sprayable powder form with from 20 to 80 parts alkali titanate from the group consisting of lithium titanate, lithium-silico-titanate, and mixtures of lithium titanate and lithium-silico-titanate in finely divided frit form,

b. Thoroughly mixing said aluminum metal powder and said alkali titanate frit to form a particulate coating mixture of uniform consistency,

c. Flowing said uniform particulate coating mixture in a temperature-elevated gaseous stream, and

d. Projecting said temperature-elevated gaseous stream containing said uniform particulate coating mixture toward said metal surface at a rate and with sufficient force to thereby impinge and adhere said particulate coating mixture on said metal surface at a substantially elevated temperature, said particulate coating mixture impinged on said metal surface at an elevated temperature forming on said metal surface an aluminum metal and alkali titanate protective coating having a surface electrical resistivity of substantially zero.

2. The method defined by claim 1 wherein said uniform particulate coating mixture composition consists of approximately 40 parts by weight of aluminum metal powder, 40 parts by weight of lithium-silico-titanate, and 20 parts by weight of lithium titanate.

3. The method defined by claim 1 wherein said uniform particulate coating mixture composition consists of approximately 50 parts by weight of aluminum metal powder and 50 parts by weight of lithium titanate.

4. The method defined by claim 1 wherein said uniform particulate coating mixture composition consists of approximately 50 parts by weight of aluminum metal powder and 50 parts by weight of lithium-silicotitanate.

5. The method defined by claim 2 wherein said lithium-silico-titanate on a calculated oxide content basis consists of lithium oxide, silicon oxide, and titanium oxide in an approximately l:l:l molecular ratio.

6. The method defined by claim 4 wherein said lithium-silico-titanate on a calculated oxide content basis consists of lithium oxide, silicon oxide, and titanium oxide in an approximately l:1:l molecular ratio. 

2. The method defined by claim 1 wherein said uniform particulate coating mixture composition consists of approximately 40 parts by weight of aluminum metal powder, 40 parts by weight of lithium-silico-titanate, and 20 parts by weight of lithium titanate.
 3. The method defined by claim 1 wherein said uniform particulate coating mixture composition consists of approximately 50 parts by weight of aluminum metal poWder and 50 parts by weight of lithium titanate.
 4. The method defined by claim 1 wherein said uniform particulate coating mixture composition consists of approximately 50 parts by weight of aluminum metal powder and 50 parts by weight of lithium-silico-titanate.
 5. The method defined by claim 2 wherein said lithium-silico-titanate on a calculated oxide content basis consists of lithium oxide, silicon oxide, and titanium oxide in an approximately 1:1: 1 molecular ratio.
 6. The method defined by claim 4 wherein said lithium-silico-titanate on a calculated oxide content basis consists of lithium oxide, silicon oxide, and titanium oxide in an approximately 1:1: 1 molecular ratio. 